Flat conductor cable (FCC) underlying carpet tiles is in present use to supply electrical power to various points of use, as for example, handling lighting and appliance loads in commercial buildings. The flat conductor cable includes in a common form thereof a plurality of flat conductors i.e., live, neutral and ground conductors encased in a plastic electrically insulative casing and additionally having a metallic shield disposed at the upper surface of the cable. A layer typically made of tough insulation material may be provided on the bottom of the cable as an abrasion protection shield. The metallic shield is electrically grounded to provide against electrical hazard, such as accidental piercing of the shield and the live conductor by an object, which object, since the shield is connected to ground, is rendered unhazardous to a person who might contact same. An advantage of the use of this type of conductor cable is the ease with which it can be installed beneath carpeting while at the same time allowing for transfer of power therefrom at selected locations, pedestals or transfer receptacles being installed for such purpose.
Various specialized types of devices including receptacles are known for establishing power take-off from the flat conductor cable at a given location as well as for effecting splicing of a branch line to a main. Thus, for connecting a receptacle at a desired location, a terminal block carrying insulation-piercing members or contacts can be secured over the flat conductor cable with the contacts piercing the flat conductor cable to establish continuity with the respective cable conductors. A receptacle can then be placed over the terminal block with suitable connection between the terminals of the block and contact points in the receptacle being made with round wire discrete conductors. With such installation the cable run can be terminated at the take-off location or it may pass through the terminal block so that additional receptacles can be connected further down the line.
It is also known to use, for purposes of providing power take-off, a receptacle which embodies insulation-piercing contacts therein and employed when installed directly over a conductor cable to have these piercing contacts electrically connectively engage the conductors in the cable. Such a receptacle is shown in commonly-assigned U.S. Pat. No. 4,479,692, issued on Oct. 30, 1984 and entitled "Receptacle for Flat Multi-Conductor Cable".
In U.S. Pat. No. 4,480,889 also commonly-assigned herewith, issued on Nov. 6, 1984 and entitled "Apparatus and Method for Tapping or Splicing Flat Multiconductor Cable", a technique and simplified device are disclosed which allow a tap or splice to be made at the same location where a flat conductor cable receptacle is present, i.e., directly under the receptacle. The device comprises a relatively elongated, thin holder of electrically insulative material having marginal configuration like that of the above-mentioned receptacle, the holder carrying insulation-piercing type contacts so arranged in such positioning, e.g., corresponding to the live, neutral and ground contact means in the receptacle, as to superpose the live, neutral and ground conductors in the branch cable when placed over the main cable during the splice installation. The insulation-piercing teeth of the respective contacts in the holder are located at both the bottom and top sides of the holder and the overall thickness of the contacts is greater than that of the holder. The holder is also provided with features such as notches and a telltale which must be properly registered with companion structure on the support member and the overlying receptacle in order to effect proper installation and orientation of the device in the intended manner. To make a splice connection, a support member is placed under the main or primary three-conductor flat cable at the location from which the splice is to be taken, the shield at the top side of the main cable is removed from over the live and neutral conductors of the cable and the holder device then placed on top of the main cable with the live, neutral and ground contacts therein in registry with the associated cable conductors. The branch, or secondary cable to be spliced to the main cable, is then superposed over the main cable, i.e., with its conductors in longitudinal registry with those in the main.
A receptacle, e.g., of the type described in U.S. Pat. No. 4,479,692 above noted, is then received on top of the branch cable and fastened with screws to the support member. Such fastening will result in the cable piercing contact portions at the bottom and top of the holder device piercing respectively, the insulation and conductors of the main cable from the top side thereof and the insulation and conductors of the branch cable from the bottom side thereof. The fastening also will result in the insulation-piercing by the receptacle contacts of the insulation of the branch conductors and coming into contact with such conductors. The run of the branch cable can then be carried out in any intended direction with the branch cable being first folded in the manner taught in U.S. Pat. No. 4,219,928 to provide that the protective shield of the branch cable is disposed at the top side of the branch.
Despite the advantages provided the flat cable system planner and installer in the foregoing developments, a difficulty which, however, remains is the efficient accomodation of the several different cable runs which are present in typical installations. Generally, the main flat cable and the primary building feeder involve a three-phase interface, i.e., the initial flat cable run is of five-conductor variety. Taps and splices to this primary flat cable are typically of single-phase (three conductor) for powering of receptacles. The taps and splices must collectively achieve a high degree of phase-balancing, whereby the respective A, B and C phases of the primary feeder are loaded to within a given percent of one another. Accordingly, the typical installation involves single-phase taps and splices to each of the three phases at hand, which taps and splices locations do not have receptacles thereat. The receptacle devices above discussed are thus operative only upon three conductor cable.